The Clinical Research Unit (CRUS)-Children's Hospital of Philadelphia (CHOP) will organize and supervise the participation of pediatric patients and their families in the projects of the Center. This unit will coordinate these research activities through the existing clinical Sickle Cell Disease Program, organized by the Division of Hematology at CHOP. This Program provides health care for approximately 550 sickle cell patients who range in age from newborn to 18 years. Patient care is supervise by a multidisciplinary team of hematologists, nurse specialists, hematology fellows, social work and administrative staff. This well-organized program will provide patients to be recruited by the CRU for the various projects of the Center. In addition to the maintenance of accurate patient records, the CRU will assist in the selection of patients for studies, provide samples, collect laboratory data, supervise all schedules for clinical projects, and coordinate all patient and family involvement in research activities of the Center. The core staff of the CRU will consist of the medical director, nurse specialist, data coordinator, social worker and clinic secretary. The CRU will also organized special diagnostic studies required for more complete characterization of patients with unusual hematologic and clinical features.